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31 maj 2020 · We are going to take a quick look at the two basic parameters you want to carefully adjust when setting up an SPI bus: Clock Polarity (CPOL) and Clock Phase (CPHA). SPI is a synchronous protocol. That means the data lines are sampled (and driven) at certain moments in time – in sync with a given clock line.
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Please refer to the device data sheet to determine the number of data bits transmitted using the SPI interface. Clock Polarity and Clock Phase. In SPI, the main can select the clock polarity and clock phase. The CPOL bit sets the polarity of the clock signal during the idle state.
SPI Timing Diagram Example. The mode depends on the SCLK level, sometimes called polarity (CPOL), when the transmission is initiated (CS is pulled low) and the sampling edge, called phase (CPHA), as shown in Figure 3. Note that the phase is relative to the polarity and is not an absolute value.
SPI timing diagram for both clock polarities and phases. Data bits output on blue lines if CPHA=0, or on red lines if CPHA=1, and sample on opposite-colored lines. Numbers identify data bits. Z indicates high impedance. The SPI timing diagram shown is further described below: CPOL represents the polarity of the clock.
The SPI interface provides the user with flexibility to select the rising or falling edge of the clock to sample and/or shift the data. Please refer to the device data sheet to determine the number of data bits transmitted using the SPI interface. In SPI, the main can select the clock polarity and clock phase.
Figure 3 shows the timing diagram for SPI Mode 1. In this mode, clock polar-ity is 0, which indicates that the idle state of the clock signal is low. The clock phase in this mode is 1, which indicates that the data is sampled on the falling edge (shown by the orange dotted line) and the data is shifted on the
These modes control whether data is shifted in and out on the rising or falling edge of the data clock signal (called the clock phase), and whether the clock is idle when high or low (called the clock polarity).
